1. Field of the Invention
The present invention relates to conductive pastes and ceramic electronic elements, and more particularly, relates to a conductive paste preferably used for forming terminal electrodes of a chip-type ceramic electronic element and to a ceramic electronic element provided with terminal electrodes formed by using the conductive paste.
2. Description of the Related Art
Heretofore, terminal electrodes used as input/output terminals or ground terminals for ceramic electronic elements are formed by, for example, applying a conductive paste to ceramic bodies by dipping or the like, drying the films thus formed and firing the dried films. The conductive paste used for this application generally comprises a conductive component, an organic vehicle and an inorganic binder such as a glass frit.
As the organic vehicle, a material comprising an organic binder, such as ethyl cellulose, nitrocellulose or an acrylic resin, as a primary component and an organic solvent, such as terpineol, 2-butoxyethanol, diethylene glycol monobutyl ether is used.
When a conventional conductive paste is applied to a ceramic body by dipping or the like and is then dried, wrinkles may be formed on the surface of the dried coating film thus formed in some cases. The formation of wrinkles is not preferable in appearance and, in addition, easily generates cracks in the terminal electrodes after firing is performed, and as a result, the reliability of the ceramic electronic element is significantly degraded.
As the reason the wrinkles are formed on the surface of the coating film, rapid evaporation of a solvent contained in the conductive paste during drying may be considered. Since the organic solvent used for the conventional organic vehicles dissolves the organic binder, the organic binder contained in the organic vehicle is precipitated when the organic solvent is evaporated. When the coating film composed of the conductive paste is dried by blowing hot air, the organic binder is precipitated on the surface of the coating film, since the solvent present in the vicinity of the surface of the coating film is preferentially evaporated in an early drying stage, and as a result, a resinous film is formed thereon. In addition, when the drying is further continued, the coating film shrinks by a volume corresponding to the amount of the evaporated solvent, but, since the surface area of the resinous film of the organic binder described above is larger than the surface area of the shrunk coating film, the resinous film is present excessively, and as a result, the wrinkles are generated on the surface of the coating film after drying is performed.
In order to prevent the generation of a resinous film of organic binder on the surface of the coating film in the early drying stage, a method may be considered in which the drying temperature is decreased or a solvent having a higher boiling point is used. However, the time required for drying is prolonged thereby, and as a result, there is a problem in that the productivity is decreased. Also, when drying is insufficiently performed, the terminal electrodes (electrode films) are likely to peel off after drying is performed.
Accordingly, the present invention was made to solve the problems described above, and an object of the present invention is to provide a conductive paste which can suppress the generation of wrinkles on electrode films after drying and can suppress the generation of cracks in terminal electrodes after firing, and in addition, another object of the present invention is to provide a ceramic electronic element having superior appearance and reliable electrical properties.
To these ends, the conductive paste of the present invention comprises a conductive component and an organic vehicle, in which the organic vehicle comprises an organic binder, a first solvent dissolving the organic binder and a second solvent not substantially dissolving the organic binder, wherein the boiling point of the first solvent is higher than that of the second solvent or is higher than the temperature at the end of distillation thereof by about 20xc2x0 C. or more, and the content of the second solvent is about 30 to 70 wt % of the organic vehicle.
In addition, the boiling point of the first solvent is preferably higher than the boiling point of the second solvent or is preferably higher than the temperature at the end of distillation thereof by about 30xc2x0 C. or more.
Furthermore, the conductive paste of the present invention may further comprise an inorganic binder.
The ceramic electronic element of the present invention comprises a ceramic body and terminal electrodes provided so as to be in contact with the ceramic body, wherein the terminal electrodes are formed of the conductive paste of the present invention described above.